The present invention relates to a bearing cap for a main bearing in an internal combustion engine. The cap consisting in part of an aluminum alloy and in part of an iron alloy forming a core in the aluminum material. The core comprises tubular portions with bores for mounting bolts and a portion, located between the tubular portions, in the area of a semi-circular supporting surface for a bearing shell.
It is known to use main bearing caps made entirely in aluminum in aluminum engine blocks to provide a design which is as light as possible. The lowest possible weight can, however, only be achieved at the cost of increased mechanical engine noise due to the greater thermal expansion of the main bearing aluminum material resulting in increased bearing clearance.
It is also known to combine low weight with reduced noise by casting an iron core in the aluminum material, so that the thermal expansion resulting in increased bearing clearance will be less than that in a bearing cap which is made entirely in aluminum. In a previously known design of the type described above by way of introduction, the iron core is made so that it forms a semi-circular surface facing the crank shaft.
When such a surface is to be machined together with its complementary semi-circular surface in an aluminum engine block, this will mean that the machine tool will work during half a revolution in aluminum and during half a revolution in cast iron. Since these materials have very different hardnesses, problems arrive with both tool selection and tool setting, which can give an unacceptable out-of-roundness and straightness of the main bearing bore.
The purpose of the present invention is to achieve a main bearing cap of the type described by way of introduction, which eliminates the problems described above in the milling of the surface of the bearing cap and the complementary surface in the engine block.